Electrical switching device



Sept. 29, 1931 w. T. WINTRINGHAM 1,324,857

ELECTRICAL SWITCHING DEVICE Filed Aug. 21. 1929 INVENTOR WZ WntlCl I/yil am BY ATTORNEY Patented Sept. 29, 1931 UNITED STATES PATENT OFFICE WILLIAM T. WINTRINGHAM, OF BROOKLYN, NEW YORK, ASSIGNOR TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK nnncrmcn. swrrcnme DEVICE Application filed August 21, 1829. Serial No. 387,425.

This invention relates to improvements in switching devices, such as keys or acks, used in communication or transmission systems, and more particularly relates to a '5 method of and means for neutralizing the effect of the capacity between the springs or members of such switching devices.

In equipment of the type utilized 1n telephone systems progressively greater difliculties are encountered due to stray capacities as the frequency of the currents transmitted over such systems is increased. For example, switching devices, such as keys or jacks of the ordinary types, may become useless at radio frequencies of, for example, ten megacycles, due to the inherent capacity between the springs of such devices. The primary object of this invention is to provide arrangements which, when applied such switching units, will tend to minimize the efiect of such capacities so that such un ts may be used freely in high frequency circuits. In the arrangements of the invention an inductance is shunted across the springs of a switching device, such as a key, to tune with the inherent capacit between the springs. As a consequence 0 this tuning, the key in its open condition more nearly represents an open circuit at the higher frequencies. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention maybe more fully understood from the following description, together with the accompanying drawings, in the Figures 1, 2 and 3 of which the invention is illustrated. Fig. 1 is a side-plan view of an ordinary switching device, such as a key or jack. Fig. 2 is a circuit diagram showing the equivalent of Fig. 1. Fig. 3 is a circuit diagram showing the arrangements of the invention. Similar reference characters have been utilized to denote like parts in all of the figures.

In Fig. 1 a typical pile-up of springs in a switching device, such as a key or jack, is shown. The springs are designated 1 and 2 and the inter-spring spacin elements are designated 3. In such a evice the two use of the key,

springs shown form the two plates of a condenser, the dielectric of which is formed in part by air and in part by the material of the inter-spring spacing elements 3. The equivalent, circuit of this pair of springs is shown in Fig. 2. At low frequencies, when the contact is open, the admittance between the springs is represented almost entirely by the conductance G. As the frequency is in creased, however, the susceptance of the capacity C between the springs increases, so that for radio or high frequencies, the total admittance islarge enough to prohibit the jack, or other open contact device of this form.

Since .the'admittance between the springs is determined largely by the susceptance of the capacity C at high frequencies, it is proposed in accordance with the arrangements of this invention as shown in Fig. 3, to shunt an inductance L between the springs to resonate with C. If the inductance has the value 1 41r f 0 the'ftotal admittance between the springs at or near the frequency f will be very small, and the resistance ofL is small, practically equalto G. In other words, in consequence of such tuning when the contacts of the springs are open, the switching device will form an anti-resonant circuit at the higher frequencies and will more nearly represent an open circuit when the key is open.

For the purpose of illustration, assume that G is equal to zero and that C is equal to 2o 1o farads. The following table shows the admittance between the springs at several frequencies:

From this table,'two facts become evident.

First, for circuits of nominal impedance (say 500 ohms) the admittance between the springs is negligible for frequencies below 100 kc. Second, at frequencies higher than 100 kc., where it would be inadvisable to 5 use the key or'other switching device, be-

cause this admittance becomes so large the inductance required to tune the capacity is M of reasonable magnitude. In the case considered, where the conductance G is assumed zero and the inductance-perfect,the admittance would fall to zeroat the resonant frequency only. In practice, however, the con.- ductance G would be of appreciablem'agnitude and also the inductance would contain resistance, so that the admittance would re- 7 main small over a finite band of frequencies.

While the invention hasbeen disclosed as I embodied in certain specific arrangements which are deemed desirable, it is understood 2) that it is capable of embodiment in many other forms without departing from the V spirit of the invention as defined by the appended claims. r hat is claimed is:

'25 1. A switching device comprising contact 7 members so positioned that an inherent capacity eifect will exist therebetween, and an inductance shunted across said contact mem- V bers and'tuned to resonate with said-capacity.

V 2. A switching device comprising contact members, and aninductanceshunted across said contact members, the valueof said in- I Y y iductance being so chosen with respect to the r I inherent capacity between said contact members that when said contact members are in open position said switching device form an anti-resonant circuit. 7 3; The method of i educing the admittance '4 in a circuit at certain frequencies due to the capacity between the contact members of a "switching device, which consists in rendering the portion of the circuit containing said contact member anti-resonantv at those certain frequencies. 7

V In testimony whereof, I have signed my 7 name to this specification this 20thday ofv August, 1929. o l V o o WILLIAM T. WINTRIN 

